This invention relates to respirators and ventilator equipment generally and in particular to an improved portable apparatus for assisting normal respiration in patients requiring such devices by the provision of both a pressure sigh and a volume sigh feature in a positive displacement respirator.
Prior portable positive displacement ventilators which have found acceptance have attempted to provide, with varying degrees of success, a so-called pressure sigh function, and some have provided a volume sigh function; but, the flexibility of reliably providing for both functions in a single unit so as to be adaptable to a large proportion of the population of ventilator users is important. Larger institutional devices employing enclosed bellows structures and the like kinds of apparatus with complex structure and controls including for example, supplemental turbine blowers, have been provided; however, these have not been easy to reduce in size effectively so the use of a portable unit has generally meant that certain desirable and often necessary features would not be present in the unit.
Further, some of the smaller positive displacement devices which have incorporated a variable volume capability have utilized either apparatus which have required the motor to be stopped during alteration of the effective radius of a crank arm which connected a connecting rod driving a piston or if designed to be run continuously have employed a variety of mechanisms for changing the effective radius of the crank arm for example, by stepwise mechanical movement of a jack screw during the revolution of the crank by means of impact engagement with mechanical activator tongs. These solutions have not been satisfactory for several reasons including the speed of the change, reliability and suitability for a variety of medical indications.
While it is desirable and therefore an objective of such devices to have continuous, reliable uninterrupted functioning of a positive displacement ventilator it is also a prime objective of such devices to be able to provide adjustment of the volume of air delivered in a predetermined timed relationship while simultaneously providing pressure protection for the patient regardless of the primary mode of function of the device.
There is extensive medical literature concerning the desirability and indeed the need for apparatus to have the capacity for an adjustable volume.
It is therefore one of the primary objectives of this invention to provide a portable ventilator respirator apparatus of the positive displacement type which reliably can provide for a pressure or a volume sigh by the provision of structure enabling the attainment of an adjustable volume or pressure while providing patient protection against excessive pressure. The foregoing is accomplished according to this invention in a rigid cylinder piston pump positive displacement respirator having means for controllably varying the length of the piston stroke from one predetermined first swept volume to another larger second swept volume and then back to the first swept volume in a timed sequential manner while providing means for preselecting a maximum delivery pressure when in either sigh cycle. Large capacity adjustable dump valves are also provided wherein a preselected timed sequential sigh can controllably be provided, wherein volume in excess of the patients requirements can be selected. For example, the ventilation pressure limit can be set to provide the required volume pressure relationship needed by the patient and dump the excess. A sigh pressure limit can also be set to provide an increased volume of air to the patient for a predetermined interval and frequency.